Acute renal failure is a serious clinical problem requiring intensive care hospitalization and dialysis. The leading cause of acute renal failure is acute tubular necrosis (ATN) of the proximal tubule due to injury after either toxicant exposure or ischemia. The physiology and molecular biology of tubular injury have been studied in detail. Yet despite this increasing knowledge base and the availability of dialysis, mortality following ATN has not improved significantly and remains around 50%. The apparent rate limiting step in the ability of patients to recover from ATN is the regeneration of the proximal tubule. Regeneration may depend on whether enough undamaged or viable proximal tubule cells remain and proliferate so that repopulation of the tubule can occur. Thus, if the available proximal tubule progenitor population could be increased, the potential for regeneration of ATN damaged tubules could be significantly enhanced. In this proposal, we examine whether embryonic stem (ES) cells can be differentiated into renal epithelial cells and whether such ES cells can be integrated into a developing kidney. The renal epithelia is derived from intermediate mesoderm and express a unique combination of genes during the early stages of kidney development. Based on our knowledge of early renal development, we will examine whether combinations of growth and differentiation factors found in the intermediate mesoderm can be used to drive ES cell differentiation along the renal epithelial lineage. ES cells will be cultured free of LIF and allowed to form embryoid bodies. These embryoid bodies will be treated with combinations of retinoids and growth factors and analyzed for the expression of renal epithelial specific genes. Once we are able to activate the appropriate battery of genes, we will dissociate the ES cell derived bodies and inject the cells into a developing kidney. The ability of ES cells to contribute to the growing kidney can then be examined by a variety of histological and immunological methods. The ability of ES derived renal progenitor cells to help alleviate ATN will then be tested in animal models. Since ES cells potentially represent an unlimited supply of renal progenitors, these experiments will lay the foundation for cell based therapies to improve the efficacy of ATN treatment.